Actually, never worked for TWA, neither did anyone in my imediate family. I am just a rather devote TWA fan (my first flight was on a TWA L1011 from Seattle to St. Louis) and have become something of a collector of TWA items and information. That list of "pigs" has come through various conversations with TWA employees and even some internet postings.
As far as I can tell, the 727s got the rather unflattering nicknames as a commentary on their handling characteristics. They had a rather peculiar tendency to wobble left and right on takeoff and landing, a fact that kept me intrigued watching them come into and out of Lambert on many occasions. I've also heard that they weren't the easiest and gentlest planes to fly, especially the later, heavier versions of the -200s.